Transfructosylated oligosaccharides such as lactosucrose have an activity of propagating bifidobacterium and currently attract attention in the fields of foods and drugs as a new sweetener that is a substitute for sucrose.
Transfructofuranosylated oligosaccharide, one of transfructosylated oligosaccharides, is usually produced by allowing .beta.-fructofuranosidase to act on a raw material such as sucrose, starch sugar, lactose, etc.
Microorganisms, such as Arthrobacter, produce .beta.-fructofuranosidase. However, said microorganisms are each low in .beta.-fructofuranosidase productivity. Therefore, there is a problem in that microorganisms must be cultivated in large amounts to produce transfructofuranosylated oligosaccharides on a large scale.
Incidentally, current progress in genetic engineering techniques has made it possible to obtain a large amount of an enzyme relatively easily even if the amino acid sequence of the enzyme has not been elucidated yet. This is achieved by isolating the gene coding for the enzyme, determining the base sequence of the enzyme, producing a recombinant DNA containing the gene coding for the enzyme, incorporating the recombinant DNA into microorganism or animal or plant cells, and cultivating the obtained transformants.
Accordingly, it has been a desire for ascertaining the gene coding for .beta.-fructofuranosidase and determining its base sequence.